Floe Formation Research Articles

Cryospheric processes in Quaternary and Cretaceous hyper‐arid plateau desert oases

AbstractWinter supercooling of oasis waters in hyper‐arid plateau deserts leads to the formation of ice floes on oases water surfaces. Multi‐year satellite imagery from recent oases in the Badain Jaran Desert (China) reveals dynamic cryospheric processes including ice floe, ice jams abutting on border ice, hinge and transverse cracks, multiple ice lobes related to aufeis formation on the ice floe surface indicating oases water level oscillations linked with short‐term variations of the groundwater input. Oasis ice floe break up and transportation by strong desert winds produce an effective gouge and abrasion mechanism of oasis margin sediments, incorporating them both into the oasis bottom, and as supra‐ice floe debris that ultimately will be released to the bottom of the oasis as dropstones as the ice cover melts. Supercooling conditions in the Badain Jarain Desert oases suggest that anchor ice can form in the oases bottoms from fazil ice crystals generated in open supercooled oasis waters. Mud dropstones and diamicton in Cretaceous wet interdune facies from China suggest ice‐rafting processes in oases. Rounded and subangular mud intraclasts are mud boudins formed by in situ boudinage of mud interdune sediments due to the combined effect of compaction by prograding aeolian sediments and aufeis formation. Anchor ice formed in the oases bottoms lifted them up due to floatability and released them as dropstones to the oasis bottom when melted. Cryospheric processes in hyper‐arid oases are more active than expected and may play a significant role in intraclast reworking. The recognition of these processes is critical for Mesozoic palaeoclimates.

Seismic Arrays on Drifting Ice Floes: Experiences from Four Deployments in the Arctic Ocean

In the last three decades our knowledge about the seismic structure and the seismicity of the world's oceans has increased tremendously through the common availability of ocean bottom seismometers for active and passive seismic studies ( e.g. , Orcutt et al. 1976; Toomey et al. 1985; Tolstoy et al. 2008). The safe recovery of the instruments is essential to access the acquired data. Comparable studies of the polar oceans do not exist, because the perennial sea-ice cover in polar regions prevents a safe recovery of ocean bottom instruments. Hence, the seismic structure and the earthquake activity of large parts of the Arctic Ocean, including the Gakkel Ridge, one of the most prominent members of ultraslow-spreading mid-ocean ridges (< 20 mm/y full rate; Dick et al. 2003), are largely unknown. Mounting conventional land seismometers on drifting sea ice is the only way to acquire seismic data in the Arctic Ocean. The difficult access to the survey area, which requires icebreaking vessels and helicopters, and the cold temperatures and a constantly moving seismometer platform, represent highly unsuitable survey conditions. However, Kristoffersen et al. (1982) made first attempts at recording regional earthquakes in the Arctic by attaching a sonobuoy array to an ice floe. Jokat et al. (2003) demonstrated that the acquisition of refraction seismic data is possible with seismic stations mounted on drifting ice floes. Okal and MacAyeal (2006) report on a deployment of seismometers on icebergs in Antarctica recording a variety of ice-induced (cryogenic) signals (MacAyeal et al. 2009). We deployed seismic arrays on drifting sea ice during four expeditions in 2001, 2007, 2008, and 2009, recording local and regional earthquakes along Gakkel Ridge. In addition, the records contained many sorts of cryogenic signals (“icequakes”) stemming possibly from collisions between ice floes, crack formation, or disintegration of ice floes …

Model of space-time dynamics of the Japan Sea ice cover

A model of space-time dynamics of the sea ice cover in which individual ice floes undergo a successive change in size is considered. The formation and melting of ice floes, their aggregation, and the formation of hummocks are taken into account. A parametric model identification is done based on a sample of ice cover area and thickness distribution in the Japan Sea.

Floe formation in Arctic sea ice

The ice pack covering northern seas is composed of a mixture of thick ridged and rafted ice, undeformed ice, and open water. Ice motions determined from satellite remote sensing data show that deformation of the pack takes place along the boundary of large floes. Eulerian continuum sea ice models can simulate this behavior to a degree by capturing the localization of gridded ice strength in some average sense. However, using a discontinuous Lagrangian approach that explicitly models ice floes and the interactions between them, it is possible to simulate both the fracture process that creates floe boundaries and the continued deformation along those floe boundaries. We have developed a granular model of the central Arctic ice pack that consists of thousands of individual grains that can freeze together, fracture apart, and interact through ridging. Accelerations produced by passing weather patterns and sustained quasi‐steady deformation cause the model pack to fracture apart into floes composed of one or more grains. When the ice pack is nonuniformly accelerating due to passage of a weather pattern, simulations show that the factors that influence the size of the floes are the tensile strength of the joints between grains, the gradient of the wind field, and the average size of the individual grains. During sustained deformation the pack continues to deform along existing floe boundaries while stresses build and further fracture takes place. In quiet areas of the basin, fractures refreeze. To explore the fracture process during sustained deformation, we run 24‐hour basin scale simulations at resolutions from 2.8 km to 14 km. At the end of each simulation we construct a distribution of floe areas. The cumulative distribution of floes at the large end of the distribution is approximately the same at each resolution. As we increase the resolution from 14 km to 2.8 km, the damage zones between large floes become more localized. A log‐log plot of the cumulative floe size distributions obtained from the simulations appears linear over several orders of magnitude.

Mechanism of solid–solid resolution of pantolactone

The enantioselective solid–solid clathration of (S)-pantolactone (1) into (R,R)-trans-2,3-bis(diphenylhydroxymethyl)-1,4-dioxaspiro[4·4]nonane (2) and -[4·5]decane (3) was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and crystal packing data. Short-distance solid-to-solid sublimation mechanisms occur in both cases with initial formation of epitaxial floes along the b-axis in 2 and random craters in 3. The bulk control in the phase rebuilding stage is understood from the particular crystal packings. Bulk control was largely lost in the phase transformation stage when passivation of the surfaces occurred in both cases. The host lattices of 2 and 3 exhibit closed molecular double layers with all hydroxyl groups inside and lacking access for intercalation of 1. The reaction has to start at isolated surface defects. Once started, new doors for further entrance of guest molecules (S)-1 are opened in the double layer. For practical use, both the crystallographic difficulties and the passivation have to be overcome. A slurry technique involving addition of stoichiometric amounts of water to the solids provided useful conditions for the preparative resolution of (R/S)-1 or further racemates exhibiting passivation, whereas heating alone speeded up the resolution of 2-methylpiperazine with 2. © 1996 John Wiley & Sons, Ltd.

Mechanism of solid-solid resolution of pantolactone

The enantioselective solid–solid clathration of (S)-pantolactone (1) into (R,R)-trans-2,3-bis(diphenylhydroxymethyl)-1,4-dioxaspiro[4·4]nonane (2) and -[4·5]decane (3) was studied preparatively and mechanistically using atomic force microscopy (AFM) measurements and crystal packing data. Short-distance solid-to-solid sublimation mechanisms occur in both cases with initial formation of epitaxial floes along the b-axis in 2 and random craters in 3. The bulk control in the phase rebuilding stage is understood from the particular crystal packings. Bulk control was largely lost in the phase transformation stage when passivation of the surfaces occurred in both cases. The host lattices of 2 and 3 exhibit closed molecular double layers with all hydroxyl groups inside and lacking access for intercalation of 1. The reaction has to start at isolated surface defects. Once started, new doors for further entrance of guest molecules (S)-1 are opened in the double layer. For practical use, both the crystallographic difficulties and the passivation have to be overcome. A slurry technique involving addition of stoichiometric amounts of water to the solids provided useful conditions for the preparative resolution of (R/S)-1 or further racemates exhibiting passivation, whereas heating alone speeded up the resolution of 2-methylpiperazine with 2. © 1996 John Wiley & Sons, Ltd.

MODELING FINES ELUTRIATION FROM A SPOUTED BED OF PULP FIBERS

A model was developed to describe the elutriation of fines from a spouted bed of pulp fibers, which is a new method to separate fines from fibers. During spouting the pulp fibers are aggregated in fiber floes, which we model as coarse porous spheres. In general, we can distinguish three liquid regions inside and around a coarse particle in a shear flow: bulk liquid, liquid passing through the sphere, and liquid circulating inside it. A system of three ordinary differential equations describing the balance of fines in these regions was solved numerically. A source term was included to account for the release of fines during the dynamic equilibrium between formation and break-up of fiber floes. Comparison between theory and experiment showed that a simplified two-region model, which contains two adjustable parameters, is adequate to describe the elutriation data.

Kinetic and Hydrodynamic Aspects of Polymer Flocculation

This article highlights the kinetic and hydrodynamic aspects of polymer-induced flocculation, as well as some of the common applications of flocculation in mineral processing. Rate equations for polymer adsorption, floe formation, floe growth and break up are summarized and analyzed. Similarly, hydro-dynamic functions relevant to the various aspects of flocculation are summarized and analyzed. Experimental results on the effects of hydrodynamic conditions on the flocculation process arc presented.

SYNTHETIC COPOLYMERS CONTAINING FREE OR PROTECTED CATECHOL RESIDUES FOR THE pH-CONTROLLED SELECTIVE FLOCCULATION OF ULTRAFINE DISPERSIONS OF ILMENITE WITH RESPECT TO RUTILE

ABSTRACT Several multifunctional polymers for the pH controlled flocculation of titanium minerals active towards ilmenite and selective respect to rutile have been prepared. They are radical vinyl copolymers containing catechol functions either free or protected and acrylic acid units. They show the distinctive property of changing their effect from flocculating to dispersing or inert and vice versa by changing pH, with great advantages for the best fulfilment of the flocculating process. The tendency of the ilmenite particles to gather, as a result of the combined effect of the cathecholic and carboxylic functions at acidic pH, is considered an essential conditions and a preliminary process for the formation of floes

Bulk Mixing Using Diffused Air in Circular and Rectangular Vessels

The use of compressed air for bulk mixing in circular and rectangular vessels has been investigated. A definition for “100% uniformity” has been postulated and correlations between the mixing time, shear gradient, and dimensionless diffuser submergence have been presented. It has been found that the mixing time in a vessel is primarily dependent on the shear gradient, G. A secondary dependence on the diffuser submergence is noted. Mixing times were measured using dye concentration versus time plots of salt and Rhodamine‐B dyes in batch experiments. Salt dye was found to produce longer mixing times for similar operating conditions. The product of the mixing time and the shear gradient has been calculated and compared to the values recommended in the literature for standard water and wastewater treatment operations. The writers' data fall below those recommended values, as expected, since only the time required for bulk uniformity and not chemical reaction, biological activity, floe formation, or gas transf...

A note on the selection of a non‐adhesive methylotrophic bacterium for use in continuous culture studies

A simple technique, based on the use of Microtitre plates, was used to select a non‐adhesive variant clone of a methylamine‐utilizing bacterium. The variant clone grew in continuous culture without visible wall growth and with only very slight floe formation, whereas the parental strain grew with very heavy wall growth and a high proportion of the suspended cells present as flocs.

Rapid brownian coagulation of colloidal dispersions.

A modified Smoluchowski theory in which the hydrodynamic interaction and Van der Waals-London potential between particles are taken into account is proposed for the rapid Brownian coagulation of colloidal dispersions and compared with experiments on coagulations of polystyrene latex particles in KC1 solutions. It is found that the theory is physically consistent with experiments and predicts the time-dependent behavior of particles for a sufficiently long time with considerable accuracy. The existence of an asymptotic particle-size distribution, the self-preserving distribution, is confirmed by experiments. These results indicate that the theory is applicable to the floe formation process where large and irregular particles are dominant, as well as to the initial stage of coagulation.

Kinetics of formation of humic substances in activated sludge systems and their effect on flocculation

AbstractHumic substances were isolated during batch aeration studies with activated sludge and a complex waste source, by using concentration and separation techniques that employ reverse osmosis, ultrafitration, and gel permeation chromatography. The study suggests that the formation of high molecular weight humic substances may occur after the removal of the readily available carbon source. The amount of refractory material finally present in the solution will depend on its adsorptive properties toward bacterial cells. The adsorptive characteristics may be determined by the magnitude of the carbohydrate fraction present in the humic substances. If the carbohydrate content decreases, adsorption onto the cells may decrease resulting in an impairment of both the floe formation and settleability of the sludge floes. Decreased adsorption will result in a higher total organic carbon content and an increase in color bearing materials in the effluent.

Microbial cell recovery enhancement through flocculation

AbstractThe removal of cellular material from fermentation broths is of importance in many fermentation processes. The present work compares the performance of recently developed polyelectrolyte flocculating additives with traditionally available additives. Objectives are to establish criteria for the choice of a flocculating additive and establish optimum conditions for the formation of stable, fast settling floe, and for quantitative separation of cellular material from the medium. Fermentation broths of actively growing Candida intermedia were used to evaluate the effectiveness of fifty commercial flocculating additives at different dosages and pH values. Certain strong anionic and strong cationic polyelectrolytes and mineral hydrocolloids were found to be most effective in their enhancement of settling rates. Some differences in behavior exist between glucose grown cells, hydrocarbon grown cells, and washed cells in buffer suspension. Flocculation of cells from fermentation broths is concluded to be highly dependent upon adsorbed material. A high charge density to interact or compete with adsorbed material and a solubility in the adsorbed material are important factors in choosing an additive for a given application. The fluid mechanics of a flocculating suspension is an important variable since low shear does not provide adequate contacting between cells for floe formation and high shear leads to floe breakup. An apparatus was constructed to grow floe under constant fluid mechanical conditions both in laminar and turbulent flow regimes. Turbulent shear was found to be very important in forming large, compact floe in cases where irreversible ionic bridging is the mechanism as for the strong anionic polyelectrolyte, polystyrene sulfonate. Adequate mixing is required to disperse the flocculating additive, but the level of turbulence is relatively unimportant in cases where reversible colloidal bridging is the mechanism as for the mineral hydrocolloid, bentonite.

Flocculation and Flocculation Basins

An important process in the treatment of water, sewage, and industrial wastes is the formation of suspended floes which can be effectively removed from the liquid by settling or filtration. This pr...

Problems in Coagulation and Corrective Treatment

Until recent years mixing basin design has been empirical, due largely to the fact that insufficient chemical engineering data were available regarding the characteristics of floe formation in its relation to time and velocity of mixing. Agitation from 15 to 30 minutes at a velocity between 1 and 1 J feet per second is necessary to produce good floe (7) in a baffled basin. Mechanical stirring requires about 40 minutes for comparable coagulation, when the initial paddle has a velocity of 2 feet per second and the last one in the series maintains a flow just sufficient to keep the floe in suspension. If this basic datum is accepted, it is at once apparent that much of the troubles experienced with poor floe formation is caused by an insufficient mixing period, since most basins in service have adequate velocities. Assuming that the correct concentration of coagulant is used and that the pH is adjusted to the proper value, coagulated floe is a dense, . compact material with well distributed silt particles throughout the mass and settles readily. An initial rapid velocity followed by a progressively decreasing speed will produce the most compact floe (4). A baffled basin having the same width of channel in all portions, or a paddle installation at equal speeds, does not produce the best coagulation. The diagram in figure 1, illustrates a round the end baffled basin designed in accordance with these newer principles. The fundamental data for this design were obtained with the laboratory stirring device under carefully controlled conditions and the rapidity of floe sedimentation was used as the criterion of good coagulation. In structural detail this design is a modification of the conventional basin as to ratio of over all dimensions and width of final passages. There are 36 channels arranged as follows :

Purification Methods at New Orleans

The purification plant at New Orleans was first put into operation in the early part of February, 1909. It was designed for a normal load of 40 m.g.d. with a maximum capacity of 60 m.g.d. The original plant consisted of two plain subsidence basins, or grit basins, with a capacity of 3.3 million gallons each; two mixing basins with a 2.5 million gallons each, which allowed one and one-half hours for mixing and floe formation; four settling basins with a combined total capacity of 30 million gallons, and a 30 million gallon clear water reservoir that was to serve as a reserve supply. The Head House, from which the entire system was controlled, and where the chemicals were stored and fed into the water, together with a filter gallery composed of ten units, each with a normal capacity of 4 million gallons, made up the system. This plant was sufficient for the City demand until the early twenties, when its capacity was taxed on a number of occasions. These periodical overloads eventually brought about the enlargement of the plant to its present size. Construction work was started in 1927, and during the latter part of 1932 the new plant plus the additional reservoirs and filters, was being entirely utilized. These additions raised the normal capacity of the plant to 112 m.g.d. The new grit basins have a capacity of 10 million gallons each, the mixing basins 4.5 million gallons each, and the four additional settling basins raise the settling capacity to 77 million gallons. Eighteen new filters were constructed, bringing the total number of these units to twenty-eight. The new plant was largely modeled after the old, the principal differences being in the equipment for handling and storing chemicals, and the method used for governing the chemical feed. In the old plant the latter was accomplished by passing the water through submerged orifice gates, the loss of head through the gates being transferred by a series of floats to a proportional head over a variable orifice, through which the chemicals in solution were fed. In the new plant this is done by using the differential of a Venturi Tube.

Mechanical Agitation and Alum Floc Formation

Our forefathers gave to the water works profession a very useful and economical chemical in alum, which has proved to be indispensable in preparing water for the rapid sand filters. The importance of mixing the water after the application of alum to produce the most effective flocculating action is well recognized. During the past years, various methods of agitation have been used, namely, baffles, hydraulic jump, flocculator and mechanical agitator. For efficient control of the mixing basins, a standard method of laboratory tests with results than can be applied to plant operations, would be of great assistance to the water works engineer. During the past five years, the writer has been making both theoretical and practical studies on the mechanical agitation phase of alum treatment. Mechanical agitation used for alum floe formation with Lake Michigan water at Winnetka, 111., was started on June 19, 1928. The original water filtration plant of 3.0 m.g.d. capacity, had one mechanical agitation basin with 10 minutes nominal detention period. The mixer assembly consisted of a three H.P. varying speed, brush shifting single phase motor, a vertical drive speed reducer and a vertical drive paddle shaft with two paddles of 8.40 square feet total surface area or 350 cubic feet basin capacity per square foot of paddle surface area. The velocities at the outer ends of the paddles were variable, 2.4 maximum and 0.95 feet per second minimum, with power consumption of 18 at maximum speed and 12 kilowatt-hours per 24 hours at minimum speed. The plant extension, put into operation on February 14, 1932, has six mechanical agitation basins with a total combined detention period of 30 minutes at plant capacity of 6.0 m.g.d. The mixer assembly consists of a two H.P. 5-speed 3-phase motor, a horizontal drive speed reducer, one set of bevel gears and a vertical drive paddle shaft. At the time these basins were put into operation, each of the six agitators had one paddle with a total square foot surface area of